The present invention relates to a recording liquid. More particularly, it relates to a recording liquid for ink jet recording or one suited for recording with hand writing instruments, and an ink jet recording method.
Hitherto, aqueous recording liquids (inks) prepared by dissolving an acid dye or direct dye in an aqueous medium or solvent type recording liquids produced by dissolving an oil-soluble dye in an organic solvent have been used as recording liquid for ink jet recording (hereinafter referred to as ink jet recording liquid). Solvent type recording liquids have the problems relating to environmental safety because of use of solvents, and their field of application is limited for inadequacy for office or home use. On the other hand, aqueous recording liquids which are most popularly used for business or domestic ink jet printers involve the problem of unsatisfactory water fastness and light fastness of the prints because of use of water-soluble pigments (dyes). The same holds true with the recording liquids for hand writing instruments.
In order to solve the above problems, there has been proposed and used in some quarters a recording liquid in which a pigment such as carbon black with excellent water fastness and light fastness is dispersed as colorant. However, the conventional recording liquids are unsatisfactory especially in respect of rubbing resistance of the prints and have the problem that the prints may be fouled when they are traced with a marker.
To overcome these problems, studies have been made on the recording liquids in which various types of polymeric material are added as binder. These recording liquids, however, have the disadvantage of being impaired in discharging stability in use because of rise of viscosity or for other reasons, and thus there has yet been available no recording liquid which can satisfy all of the essential requirements, i.e. stability of jetting performance, print density, rubbing resistance and tolerance to marker. Especially when a printing is to be used for a specific purpose such as presentation as a bulletin, the recording method is used primarily in which recording is made on a special recording sheet having an ink receiving layer on the support such as paper or resin film by an ink jet printing system. In this case, when it is tried to obtain good ink jettability and storage stability, there tend to arise the problem that rubbing resistance and gloss of the prints become unsatisfactory in the case of glossy paper having a smooth surface, whilst the print density lowers in the case of matte paper with high surface roughness.
As a result of the present inventors' earnest study to solve the above problems, it has been found that the above problems can be easily attained by containing a specific polymeric material in a pigment-dispersed recording liquid and determining the optimal range of surface tension of the said recording liquid.
The present invention has been attained on the basis of the above finding.